  {  Petrova Tatjana
     2012/09/24
     This program can say if this polygon is convex.}

program ConvexPolygon;

{$APPTYPE CONSOLE}

uses
  SysUtils;

var
  a,d,  i : integer;
  fin : textfile;
  mass,mass1,mass2 : array of integer;

begin
  assignFile(fin, 'input.txt');
  reset(fin);
  readln(fin,a);
  Setlength(mass,a);
  Setlength(mass1,a);
  Setlength(mass1,a-2);
  for i:= 1 to a do
  begin
    readln(fin,mass[i],mass1[i]);
  end;
  closeFile(fin);
  for i:=0 to (a-3) do
  begin
    mass2[i]:=-mass[i]*mass1[i+1]+mass[i+1]*mass1[i]-mass[i+1]*mass1[i+2]+mass[i+2]*mass1[i+1]-mass[i+2]*mass[i]+mass[i]*mass1[i+2] ;

  end;
  d :=-mass[0]*mass1[a-1]+mass[a-1]*mass1[0]-mass[a-1]*mass1[a-2]+mass[a-2]*mass1[a-1] -mass[a-2]*mass1[0]+mass[0]*mass1[a-2];
  for i := 0 to a-3 do
  begin
    if (d>0) then 
    begin
      if (mass2[i]<0) then
      begin
        writeln('No!');
        readln;
        break;
      end
    end else begin
      if (mass2[i]>0) then
      begin
        writeln('No!');
        readln;
        break;
      end;
    end;
  end;
  writeln('Yes');
  readln;

end.



